Missing values in ethnicity are handled by (i) a CRA, (ii) single imputation with the White ethnic group, (iii) standard MI, and (iv) calibrated-\(\delta \)  adjustment MI using the 2011 ONS census distribution of ethnicity in London [1]} as the reference distribution. For MI of ethnicity, a multinomial logistic regression imputation model is constructed for ethnicity using all variables in the analysis model, including individuals' age group in 2013, sex, and quintiles of the Townsend score. In MI, the outcome variable must be explicitly included in the imputation model for the incomplete covariate. [2]} Since the analysis model is a logistic regression model, the type 2 diabetes indicator is also included as a covariate in the imputation model for ethnicity.
